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Inside the Box

All About Blossom End Rot

May 26, 2017 at 8:08 AM / by EarthBox Sales & Marketing

EarthBox Sales & Marketing


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If you’ve ever grown tomatoes, it’s likely that you’ve had the unfortunate experience of watching your fruit rot on the vine—you may have had the most perfect little tomatoes setting all over, only they start turning brown, eventually to an ulcerous black color—and quite literally, the fruits of your labor are wasted. After experiencing such disappointment, frustration, and defeat, who could blame you if you vowed to never garden again?

Maybe you thought your plants were diseased, or perhaps you were a budding gardener with little experience and thought it was normal. Maybe a neighbor told you that you had “bottom rot” which sounds offensive, and you didn’t bother to look into it.

Well, it turns out that your neighbor was sort-of right. “Blossom End Rot,” also known as BER, is a plant disorder that affects Nightshade crops: eggplants, peppers, and especially tomatoes. Not to be confused with a systemic disease such as Blight, which is fatal to your plant, this common disorder is not transmitted through the air or by a vector…BER occurs naturally when the plant is stressed, and can be corrected if caught early.

Before you throw in the towel and declare yourself to have a black thumb, read on to learn more about what you can do to prevent and treat Blossom End Rot.


  Identifying BER

When tomato fruits and buds begin to set, they look like tiny pale green peas, with their signature yellow flowers attached at the bottoms. The flower will eventually shrivel, turn brown, and fall off as the fruit (the tomato) develops. This is known as the “blossom end” of the fruit.

To find out if your plant has BER, simply look at the blossom ends of several fruits. In the early stages, young fruit will appear to have what resembles a dark water stain on the blossom end. If it goes unnoticed, eventually that stain will start pitting and turning brown. If you see some fruit ripening too early, take a close look at the blossom end—chances are it’s advanced BER: the bottom half of the tomato is black and concaved, and the fruit is mushy.

  Causes of BER

These three main causes of stress in Nightshades are usually to blame for the development of Blossom End Rot:

  1. Insufficient nutrients
  2. Inconsistent or inadequate watering
  3. Rapid growth of the plant

If you’re thinking to yourself “I followed the EarthBox® instructions and I still got BER,” there are a few factors to take into consideration:

  • If this is a new set-up of an EarthBox® system, the dolomite can take longer to break down for the calcium and magnesium to become readily available to the plant.
  • Are you keeping the water reservoir full? Tomatoes are incredibly thirsty plants, and it’s common for just two indeterminate tomatoes in the EarthBox® gardening system to drink 6-10 gallons of water per day. A constant supply of water is best, otherwise be sure to fill the reservoir in the morning and the evening.
  • Because plants constantly have a healthy supply of nutrients and water when growing in the EarthBox®, rapid growth is nearly unavoidable and, with most crops, a good thing for a large harvest.

  Prevention & Treatment for BER

There are a few things EarthBox® gardeners can do to help prevent Blossom End Rot on their tomatoes. This means giving your plants some extra attention, but you should be inspecting your crops daily for disease, insect damage, and evidence of other pests anyway.

  • Don’t Start Over Each Season

You can, and should, reuse your growing medium for 8-10 growing seasons, sometimes longer. There is no reason to discard your growing medium each year when you want to replant. Even if your previous crop was diseased, you may still be able to use it if the disease could not withstand a killing frost (confirm any diseases with a soil sample test from your county extension service). If you enjoy starting fresh each year, simply turn your system out onto a tarp or in a wheelbarrow to break up any roots and add in some fresh growing media. If desired, you can take this opportunity to clean out the water reservoir and inspect the system, then set it up according to the instructions.

  • Always Add Dolomite

Dolomite is mined limestone that contains both calcium and magnesium, which are critical elements for the development of healthy tomatoes. This essential ingredient should not be overlooked if you want a successful tomato crop. Each year that you re-use the same growing medium, you are allowing the residual dolomite to break down and become that much more concentrated and available to your tomato plants—which helps reduce the occurrence of BER.

  • Get an Early Start

If you’re itching to get outside to get a head start on your garden, go ahead! Keep in mind your USDA Hardiness Zone may not be frost-free yet (or it might still be too hot in southern regions), so we don’t recommend actually planting your crops. But preparing your EarthBox® systems early will reward you later on when it’s time to get your plants in—not only will you be thanking yourself for saving time down the road, but adding the dolomite from your Replant Kit a couple months early will allow it to start breaking down, making key nutrients more available when you do put your plants in, thus reducing the plants’ risk of developing Blossom End Rot. .

  • Use the Right Fertilizer

Using the EarthBox® Replant Kit each season is not just convenient, but it provides the right amount of balanced plant food, in addition to the dolomite and new mulch cover (which helps conserve water for those thirsty plants!). Any plant that yields fruit—tomatoes, peppers, zucchini, eggplant, cucumbers—should be given fertilizer that contains a higher amount of phosphorus (P) and potassium (K). Fertilizer high in nitrogen (N) yields a lot of foliar growth, which is required for growing healthy leaves to help shade growing fruit from the sun, but is better suited for growing herbs and leafy green vegetables. Phosphorus helps boost blossom and fruit development, and potassium helps the overall health and functions of the plant. Likewise, overfertilizing or using a blend that is too strong can be counterproductive and also cause BER.

  • Consider Using a Supplement

Dr. Gary R. Bachman, a Horticulturist and long-time user of the EarthBox® gardening systems at his Heritage Cottage Urban Nano Farm, discovered years ago that adding calcium nitrate to the EarthBox® water reservoir could significantly reduce the occurrence of Blossom End Rot, as well as improve the health of the plant. Calcium nitrate, or "The Snack" as he calls it, dissolves quickly in water and provides tomato plants with an extra boost of readily available calcium. To use, add one teaspoon of calcium nitrate down the water fill tube each week.

  • Treat Tomatoes Right Away

In the event your plants still develop BER, don’t fret. There is a quick, inexpensive remedy that usually corrects the disorder within a few days. The earlier you identify Blossom End Rot, the more likely this will help. Carefully remove and discard any affected fruit. At dusk, carefully tip the system towards the overflow drain and let any water out. Mix ¼ cup of Mrs. Wages Pickling Lime with one gallon of water, and add it to the reservoir. The next morning, resume watering as usual and start a weekly treatment of calcium nitrate. It can take several days for this treatment to work, so you might still see some affected fruit. This should decrease over a period of 1-2 weeks. Don’t use this treatment more than one time, as the buildup of too much hydrated lime can cause the roots of your plants to burn.

  • Plant the Right Type of Tomatoes

Some tomatoes, such as paste tomatoes, are more prone to developing BER. Before growing, do a little research and look for varieties, like cherry tomatoes, that are unlikely to develop this disorder.

  • Provide Shade for Your Tomatoes

If you've tried everything and are still having problems, take temperatures into consideration. It's true that tomatoes are warm weather crops and need consistently warm-hot weather to grow big and healthy, but even they have their limits when it comes to direct sun and heat. When tomato plants are stressed from heat or insufficient watering, they tend to pull all their available nutrientsincluding calcium and magnesium–into their stems and leaves away from the fruit so they can keep growing. Do your plants a favor and move them to a shaded area when it's blazing hot outside, or set up a retractable shade cloth that can be used to give them a little break.


Tell us in the comments: What rememdies do you use to grow an abundance of tomatoes?

Topics: Garden Info, Helpful Hints

EarthBox Sales & Marketing

Written by EarthBox Sales & Marketing

Since 1994, EarthBox® has been the pioneer in container gardening. The patented EarthBox® gardening system was developed by commercial farmers and has been proven in both the lab and on the farm. This maintenance-free, award-winning, high-tech growing system controls soil conditions, eliminates guesswork, and more-than-doubles the yield of a conventional garden; all with less fertilizer, less water and virtually no effort!